Organic compounds which are able to form lipophilic complexes with cations, like certain dicarboxylic acid diamides, are frequently used for the determination of cations in sample solutions. For example, corresponding ion selective parts like ion selective membranes of ion selective electrodes which contain as a component the organic compound which is able to form the complex with the cations are frequently used for the determination of the concentration of said cations in sample solutions. Corresponding equipment for the determination of the concentration of sodium ions, potassium ions and calcium ions in body fluids, like whole blood or blood serum, have been used for several years in the clinical field for the determination of said cations.
Furthermore, test devices are known in the art which contain said cation selective complex forming organic components are well as an indicator; for instance a pH indicator, in a carrier material or on a carrier material.
In said test devices an alternation of a property of the indicator is determinable, for instance a colour change of the indicator, if the test devices are contacted with a sample solution which contains the cation to be determined.
Contrary to this, in the prior art only a few organic compounds are described which have the ability of selectively interacting with anions and are useful as ion selective components for the determination of the stated anions in sample solutions, e.g. a quantitative or semiquantitative determination of the concentration of the anions in said sample solutions.
It was the aim of the present invention to select from compounds which are already described in the prior art, such compounds which are able to interact selectively with anions of oxa acids, respectively to provide new compounds which have the ability of interacting with anions of oxa acids.